Increased vesicle endocytosis due to an increase in the plasma membrane phosphatidylserine concentration

Endocytosis vesiculation consists of local membrane invaginations, continuously generated on the plasma membrane surface of living cells. This vesiculation process was found to be activated in vivo by the generation of a transmembrane surface area asymmetry in the plasma membrane bilayer, after enhancement of transbilayer phospholipid translocation. The observed enhancement was shown to be in good quantitative agreement with a theoretical model of elastic equilibrium describing stabilization of 100-nm vesicles in response to phospholipid redistribution. Very rapid dynamic vesiculation and direct re-fusion of the vesicles, both dependent on the phospholipid translocation activity, were found on a time scale of seconds. Both vesiculation and re-fusion were shown to result in a steady-state population of internal vesicles at long time points. The plasma membrane appears to be a dynamic structure, oscillating between two distinct curvature stales, the 10 mu m(-1) ''vesicle'' and the 0.1 mu m(-1) ''plasma membrane'' curvature states, This dynamic behavior is discussed in terms of an elastic control of the membranes curvature state by the phospholipid translocation activity.